In the art of pavement markers, it has previously been common to first mold a top member with an open window for framing in edge overlapping relationship a separately molded plastic lenticular retro-reflective flattened reflector. After the reflector is duly positioned in the window on the back side of the molded top member, a liquified hardening plastic is poured into the back cavity and allowed to harden. The top member with assembled reflector and the hardening plastic can be maintained in a mold during this back side formation process, thereby permitting, if desired, a pattern to be impressed upon the generally flat resulting back face. Such a pattern is intended to enhance marker back face bonding to an adhesive located on the pavement surface.
Unfortunately, this type of pavement marker and the associated method of making suffers from various serious disadvantages. One disadvantage is that the liquified hardening plastic commonly used was an epoxy resin of the bisphenol A/epichlorohydrin type. Epoxy resins have now been found to be undesirable for usage under field conditions such as occur in the marker use environment where such a resin deteriorates and degrades with time resulting in the release to the environment of by-products considered to be undesirable and objectionable.
Another disadvantage is that the liquified hardening plastic tends to degrade the reflector retro-reflective characteristics when placed into direct contact with the reflector back face such as occurs particularly during the molding process. The reflector back face contains molded thereinto the critical facet surfaces by which retro-reflectivity of incident light upon the reflector front face is achieved, as is well known in the art. It was therefore necessary to protect the reflector back face with a separately preliminary applied coating or the like which increased pavement marker manufacturing time and cost.
Another disadvantage is that the resulting so made reflectorized pavement marker tended to have a short useful life even when used only in non-freezing road applications because of the tendency for water and moisture to penetrate around perimeter edges of the back face protected reflector and to interfere with retro-reflectivity owing to small apertures that characteristically existed between reflector edges and adjacent portions of the top member.
The art needs a new and improved pavement marker structure and an associated new method of manufacture which avoids such disadvantages.